Method of forming electronic device that includes forming protective package to house substrate and die attached thereto while leaving first and second active surface portions of the die exposed

ABSTRACT

Electronic device including a substrate provided with at least one passing opening, a MEMS device with a differential sensor provided with a first and a second surface having at least one portion sensitive to chemical and/or physical variations of fluids present in correspondence with a first and a second opposed active surface thereof. The first surface of the MEMS device leaving the first active surface exposed and the second surface being provided with a further opening which exposes said second opposed active surface, the electronic device being characterized in that the first surface of the MEMS device faces the substrate and is spaced therefrom by a predetermined distance, the sensitive portion being aligned to the passing opening of the substrate, and in that it also comprises a protective package, which incorporates at least partially the MEMS device and the substrate.

PRIORITY CLAIM

The present application is a Continuation of U.S. patent applicationSer. No. 12/508,869 filed Jul. 24, 2009, now U.S. Pat. No. 8,134,214issued Mar. 13,2012; which application is a Continuation-In-Part ofInternational Application Serial No. PCT/EP2008/000495, filed Jan. 23,2008, which claims the benefit of Italian Patent Application Serial No.MI2007A000099, filed Jan. 24, 2007; all of foregoing applications areincorporated herein by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present disclosure relate to an electronic devicecomprising MEMS devices and drilled substrates, in particular of theland grid array (LGA) or ball grid array (BGA) type.

Embodiments of the disclosure particularly, but not exclusively, relateto an electronic device comprising MEMS differential sensors mounted ona LGA substrate, wherein the MEMS differential sensor needs a doublephysical interface of communication with the environment outside theelectronic device and the following description is made with referenceto this field of application by way of illustration only.

BACKGROUND

As it is well known, a MEMS device (micro-electro-mechanical system) isa micro device which integrates the mechanical and electrical functionsin a silicon chip or die by using the lithographic techniques of micromanufacturing.

In particular, with reference to FIG. 1, a MEMS differential pressuresensor 100 is described which comprises a silicon die 101 formed by anannular portion 102 and a circular or squared membrane 103 coupled tothe upper edge of the annular portion 102.

The lower edge of the annular portion 102 is coupled to a protectivepackage 104 of plastic, metallic or ceramic material by means of anadhesive layer 105.

The protective package 104 is formed by a housing, substantially cupshaped housing, which shows an internal cavity 106 wherein the die 101is mounted. The protective package 104 is also provided with a passingopening 107. When the die 101 is mounted in the cavity 106, the annularportion 102 surrounds the passing opening 107, thereby the passingopening 107 realizes a first access gate of a first pressure P1 onto thelower surface of the membrane 103.

In a conventional way, the protective package 104 is realized throughmolding before the die 101 is glued inside the cavity 106.

The cavity 106 is then closet on top by a metallic or plastic cover 108provided with an opening 109 for putting the cavity 106 in communicationwith the outside of the protective package 104.

In particular, this opening 109 realizes a second access gate for asecond pressure P2 onto the upper surface of the membrane 103. The MEMSdifferential pressure sensor 100 is then able to measure differences ofpressure between the first and the second pressure P1, P2.

Moreover, metallic pins 110 project from the protective package 104 forallowing the electric connection of the MEMS differential pressuresensor 100 with the outside of the protective package 104.

Connections 111 for electrically connecting the die 101 with themetallic pins 110 of the cavity 106 are realized though wire bonding,after the die 101 has been fixed in the cavity 106.

A protective coating layer 112, generally silicon gel, fills in almostcompletely the cavity 106.

In other known embodiments, also the cover 108 is formed through moldingand coupled to the protective package 104 after that the MEMSdifferential pressure sensor 100 has been fixed in the cavity 106 andelectrically coupled to the pins 111.

Although advantageous under several aspects, these embodiments of theassembled electronic devices comprising MEMS differential pressuresensor show the drawback of being cumbersome since the cavity 106 shouldbe wide enough for housing the die 101 and allowing the alternativeconnection operations through wire bonding.

Therefore the manufacturing of these devices provides the followingsteps: manufacturing of the protective package 104 and of the cover 108,mounting and electric connection of the die 101 inside the protectivepackage 104, mounting of the cover 108 on the protective package 104.

Since these process steps are not provided in the conventional processflow for the realization of integrated circuits cause a considerableincrease of the costs of the final device.

The technical problem underlying embodiments of the present disclosureis that of devising an electronic device comprising MEMS differentialsensor devices, having such structural characteristics as to realizethis electronic device with manufacturing processes of conventionalintegrated circuits, overcoming the limits and/or drawbacks stilllimiting conventional electronic devices.

SUMMARY

A first embodiment of the present disclosure relates to an electronicdevice comprising a substrate having at least one passing opening; adifferential sensor MEMS device having at least a first and a secondsurface leaving exposed a first and second active surface, respectively;a protective package incorporating at least partially said MEMS deviceand said substrate so as to leave exposed said first and second activesurfaces; said differential sensor being sensitive to chemical and/orphysical variations of fluids getting in contact with said first and/orsecond active surface; said first surface of said MEMS device facingsaid substrate and being spaced from said substrate by a distance; saidsecond surface being opposed to said first surface and having an openingfor exposing said second active surface; said sensitive portion beingaligned with said passing opening of said substrate.

The characteristics and the advantages of the electronic deviceaccording to embodiments of the disclosure will be apparent from thefollowing description of an embodiment thereof given by way ofindicative and non limiting example with reference to the annexeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In these drawings:

FIG. 1 is a sectional view of an embodiment of an electronic devicecomprising conventional MEMS differential pressure sensor devices,

FIG. 2 is a sectional view of an electronic device comprising MEMSdevices according to an embodiment of the disclosure,

FIG. 3 is a sectional view of a first version of the electronic deviceof FIG. 2,

FIG. 4 is a sectional view of a second version of the device of FIG. 2,

FIG. 5 is a sectional view of a third version of the device of FIG. 2,

FIG. 6 is a sectional view of an electronic device comprising MEMSdevices according to a second embodiment of the disclosure,

FIG. 7 is a sectional view of an electronic device comprising MEMSdevices according to a third embodiment of the disclosure,

FIGS. 8 and 9 are sectional views of applications of the electronicdevices comprising MEMS devices realized according to embodiments of thedisclosure,

FIGS. 10 and 11 are sectional views of known MEMS differential pressuresensors.

DETAILED DESCRIPTION

The following discussion is presented to enable a person skilled in theart to make and use the disclosure. Various modifications to theembodiments will be readily apparent to those skilled in the art, andthe generic principles herein may be applied to other embodiments andapplications without departing from the spirit and scope of the presentdisclosure. Thus, the present disclosure is not intended to be limitedto the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

With reference to FIG. 2, a first embodiment is shown of an electronicdevice 1 for MEMS differential sensor devices according to embodimentsof the disclosure which comprises a substrate 2, for example of theLGA/BGA type, having an upper surface 3 and a lower surface 4 opposed tothe upper surface 3, provided with a passing opening 5 between these twosurfaces 3, 4.

In a known way a substrate of the LGA/BGA type is formed by conductivelayers insulated from each other by means of layers of insulating ordielectric material. The conductive layers are conformed in conductivetracks insulated form each other by layers of insulating or dielectricmaterial. Conductive holes, called “vias”, are typically realizedthrough the insulating layers with a vertical orientation with respectto the layers, to form conductive paths between conductive tracksbelonging to different conductive layers.

Moreover, lands 6, coupled to conductive tracks present on the lowersurface 4, are present on the lower surface 4 of the substrate 2.

The electronic device 1 also comprises a MEMS differential sensor device7 comprising a die 8, for example of silicon, having a first surface 9and a second surface 10 opposed to the first surface 9. On the firstsurface 9 a sensitive portion 11 of the MEMS differential sensor device7 is integrated which leaves a first active surface 11 a of thesensitive portion 11 exposed, while the second surface 10 is providedwith an opening 12 which exposes a second active surface 11 b, opposedto the first active surface 11 a, of the sensitive portion 11.

According to embodiments of the disclosure, the first surface 9 of theMEMS differential sensor device 7 faces the upper surface 3 of thesubstrate 2 and is spaced therefrom by a determined distance and thesensitive portion 11 aligned to the opening 5.

Moreover, the peripheral portion of the first surface 9 of the MEMSdifferential sensor device 7 is provided with lands for the electricconnection to conductive tracks present on the upper surface 3 of thesubstrate 2, by means of electric connections 13, for example bumps.

Advantageously, the MEMS differential sensor device 7 is electricallymounted on the substrate 2 by means of the known “flip-chip” assemblingmethod.

Still according to embodiments of the disclosure, the electronic device1 comprises a protective package 14, realized through molding, whichincorporates the MEMS differential sensor device 7, the electricconnections 13 and the substrate 2, leaving the first active surface 11a of the sensitive portion 11 of the MEMS differential sensor device 7exposed through the passing opening 5 and the second active surface 11 bof the sensitive portion 11 exposed through the opening 12 of the secondsurface 10.

Advantageously, the protective package 14 leaves also the lower surface4 of the substrate 2 exposed.

Advantageously, the second surface 10 of the MEMS differential sensordevice 7 is flanked to an upper surface of the protective package 14.

According to embodiments of the disclosure, the sensitive portion 11 issensitive to chemical and/or physical variations of fluids present on orgetting in contact with the two active surfaces 11 a, 11 b of thesensitive portion 11. The fluids can be at least two, in such a case afirst fluid interacts with the first active surface 11 a of thesensitive portion 11 of the MEMS differential sensor device 7 throughthe passing opening 5, and the second fluid interacts with the secondactive surface 11 b of the sensitive portion 11 of the MEMS differentialsensor device 7 through the opening 12 provided on the second surface10.

Advantageously, a barrier element 15 is positioned between the firstsurface 9 of the MEMS differential sensor device 7 and the upper surface3 of the substrate 2 so as to surround said sensitive portion 11.

Advantageously according to embodiments of the disclosure, the presenceof this barrier element 15 protects the sensitive portion 11 during themanufacturing process of the protective package 14, though molding, sothat this sensitive portion 11 remains free.

In fact, in a known way, the formation of the protective package 14provides the introduction, inside a cavity of a mold, of the substrate 2whereon the MEMS differential sensor device 7 is mounted.

In the mold cavity the injection is then provided, under pressure and athigh temperature, of an electrically insulating material being melted,which will constitute the plastic body of the protective package 14.This material is typically a synthetic resin, for example an epoxyresin.

The proper molding step involves the injection of the resin into thecavity of the mold. This step is then followed by a cooling step forcompleting the protective package 14.

For avoiding that the resin damages the sensitive portion 11 of the MEMSdifferential sensor device 7 during the injection step of the resin,according to embodiments of the disclosure, between the upper surface 3of the substrate 2 and the first surface 9, the barrier element 15 isprovided which completely surrounds at least the sensitive portion 11 ofthe MEMS differential sensor device 7.

Advantageously, the barrier element 15 is a ring which completelysurrounds the sensitive portion 11 of the MEMS device 7, when the MEMSdevice 7 is mounted on the substrate 2, and contacts the upper surface 3of the substrate 2 and the first surface 9 of the MEMS differentialsensor device 7.

Advantageously, the barrier element 15 is formed by a welding paste,thereby, in this embodiment, the electric connection step and the gluingstep of the MEMS differential sensor device 7 to the substrate 2 arecarried out at the same time, resulting in a particularly compactstructure of simple realization, not needing critical alignments betweendifferent structures.

Moreover, the external edge of this barrier element 15 is, for example,completely incorporated in the protective package 14.

With reference to FIG. 3, a first embodiment is shown of an electronicdevice 1 a according to embodiments of the disclosure.

Elements being structurally and functionally identical with respect tothe electric device described with reference to FIG. 2 will be given thesame reference numbers.

Advantageously, a barrier element 15 a is positioned at least in an areawhich surrounds the sensitive portion 11.

In this first embodiment, the barrier element 15 a is an irregular area15 a formed on the upper surface 3 of the substrate 2.

Advantageously, this irregular area 15 a shows a corrugated surface.

Advantageously, this irregular area 15 a extends on the upper surface 3of the substrate 2 in correspondence with the whole central free area.

Advantageously, according to embodiments of the disclosure thisirregular area 15 a is obtained by modifying the chemical properties ofthe upper surface 3 of the substrate 2, as shown in FIG. 3.

Advantageously, the irregular area 15 a is formed by a non wettablematerial.

Nothing forbids that this layer 15 a of non wettable material is formedon the upper surface 3 of the substrate 2.

With reference to FIG. 4, a second version of the embodiment of anelectronic device 1 b according to embodiments of the disclosure isshown.

Elements being structurally and functionally identical with respect tothe device 1 described with reference to FIG. 2 will be given the samereference numbers.

Advantageously, a barrier element 15 b is positioned at least in an areawhich surrounds the sensitive portion 11.

In this second version, the barrier element 15 b is an irregular area 15b formed on the first surface 9 of the MEMS differential sensor device 7and is obtained by modifying the chemical properties of the firstsurface 9 of the MEMS differential sensor device 7.

Advantageously, this irregular area 15 b extends on the first surface 9of the MEMS differential sensor device 7 in correspondence with thewhole sensitive portion 11 of the MEMS differential sensor device 7.

It is in fact known that a silicon die 8, at least in correspondencewith the first surface 9 of a MEMS differential sensor device 7, iscoated by an insulating layer 9 b of the non wettable type coated by aprotection layer 9 a comprising wettable material for example a plasticlayer, for example comprising organic material such as Polyimide.

Advantageously, at least in correspondence with the sensitive portion 11of the MEMS differential sensor device 7, the layer of wettable material9 a is removed leaving the insulating layer 9 b, for example formed bysilicon oxide, exposed.

Advantageously, after the removal step from the sensitive portion 11 ofthe MEMS differential sensor device 7 of the layer 9 a of wettablematerial, the MEMS differential sensor device is welded onto thesubstrate 2 and is subjected to a cleaning operation, for example inPlasma, by using a gas mixture including argon and oxygen.

Advantageously, the oxygen of the cleaning mixture chemically reactswith the layer 9 a of wettable material increasing the wettability,while the dielectric layer 9 b which coats the sensitive portion 11 isinert to the treatment.

Therefore, as result after the treatment, an increased wettability isobtained of the layer 9 a of wettable material, comparable to that ofthe upper surface 3 of the substrate 2 and a reduced wettability of thesurface of the dielectric layer 9 b which coats the sensitive portion11.

This wettability difference implies a sudden slow down of the resin flowduring the molding step of the protective package 14 thereby thesuperficial voltage of the resin leads to the formation of a meniscusaround the peripheral surface of the dielectric layer 9 b which coversthe sensitive portion 11.

Nothing forbids that a barrier layer 9 b of non wettable material isformed not only on the first surface 9 of the MEMS device, but also onthe upper layer 3 of the substrate 2 aligned to the sensitive portion11.

In a further version of these two latter embodiments of the disclosurethe irregular area 15 a, 15 b shows wrinkles.

Advantageously, in the irregular area 15 a, 15 b trenches are formed,made in the substrate or in the MEMS differential sensor device 7, so asto realize a preferred path defined in the substrate 2 or on the MEMSdifferential sensor device 7 for the resin during the molding step.

Advantageously, these trenches completely surround the sensitive portion11 of the MEMS device 7, as shown for example in the device 1 c of FIG.5, wherein elements being structurally and functionally identical withrespect to the device 1 described with reference to FIG. 2 have beengiven the same reference numbers.

Advantageously, in this latter embodiment a layer of non wettablematerial can be present in correspondence with the sensitive portion 11of the MEMS differential sensor device 7 in correspondence with the areaenclosed by the trenches, both on the substrate 2 and on the MEMSdifferential sensor device 7.

According to embodiments of the disclosure, the presence of thisirregular area 15 a, 15 b protects the sensitive portion 11 during themanufacturing step of the protective package 14, through molding, sothat the liquid resin is uniformly distributed around the electricconnections without reaching the sensitive portion 11.

With reference to FIG. 6, a second embodiment of an electronic device 1d according to embodiments of the disclosure is shown.

Elements being structurally and functionally identical with respect tothe device 1 described with reference to FIG. 2 will be given the samereference numbers.

In particular in this embodiment an underfiller 16 incorporates theelectric connections 13 to mechanically strengthen the electronic device1 in the connection area between the MEMS differential sensor device 7and the substrate 2.

Advantageously, the underfiller 16 is formed by epoxy compounds, forexample epoxy resin.

Advantageously, a barrier element 15 can be provided between the MEMSdifferential sensor device 7 and the substrate 2.

Advantageously, the underfiller 16 shows a tapered profile outwards ofthe MEMS differential sensor device 7, while it shows a substantiallyvertical profile in correspondence with the barrier element 15.

In other words, the cross section of the underfiller 16 increases whenapproaching the upper surface 3 of the substrate 2.

The electronic device 1 d also comprises a protective package 14 d,realized through molding, which incorporates the MEMS differentialsensor device 7, the underfiller 16 and the substrate 2, leaving thefirst active surface 11 a of the sensitive portion 11 of the MEMSdifferential sensor device 7 exposed through the passing opening 5 ofthe substrate 2 and the second active surface 11 b exposed through theopening 12 of the second surface 10.

Advantageously, the protective package 14 d leaves also the lowersurface 4 of the substrate 2 exposed.

Advantageously, the second surface 10 is flanked to an upper surface ofthe protective package 14 d.

The presence of the barrier element 15 allows maintaining the sensitiveportion 11 of the MEMS differential sensor device 7 free from theunderfiller 16.

Moreover, the underfiller 16 protects the first surface 9 of the MEMSdifferential sensor device 7 during the manufacturing step of theplastic package 14 d.

Advantageously, the underfiller 16 is present outside the barrierelement 15 a, 15 b of the embodiments described with reference to FIGS.3, 4 and 5, at least in the area comprised between the upper surface 3of the substrate 2 and the first surface 9 of the MEMS differentialsensor device 7 so as to incorporate the electric connections 13 formechanically strengthen the electronic device 1 in the connection areabetween the MEMS differential sensor device 7 and the substrate 2.

With reference to FIG. 7, a third embodiment of an electronic device 1 eaccording to embodiments of the disclosure is shown.

Elements being structurally and functionally identical with respect tothe device 1 described with reference to FIG. 2 will be given the samereference numbers.

The electronic device 1 e also comprises a protective package 14 e,realized through molding, which incorporates the MEMS differentialsensor device 7 and the substrate 2, leaving the first active surface 11a of the sensitive portion 11 of the MEMS differential sensor device 7exposed through the passing opening 5, and advantageously, the lowersurface 4 of the substrate 2. The protective package 14 e coats thesecond surface 10 of the MEMS differential sensor device 7 and isprovided with a further passing opening 17 aligned to the opening 12present on the second surface 10 of the MEMS differential sensor device7.

Advantageously, a cylindrical projection 18 is formed on the passingopening 17 of the protective package 14 e to facilitate the access tothe sensitive portion 11 of the MEMS differential sensor device 7.

Advantageously, this cylindrical projection 18 is realizedsimultaneously with the protective package 14 e during the same moldingstep in which this package is formed.

Advantageously, a barrier element 15 can be provided between the MEMSdifferential sensor device 7 and the substrate 2.

Advantageously, also in this embodiment of the disclosure the barrierelements 15 a and 15 b shown with reference to FIGS. 3 to 5 or anunderfiller 16 like the one shown with reference to FIG. 6 can beprovided.

With reference to FIG. 8, the device 1 of FIG. 2 is shown wherein anintegrated circuit 19 is mounted on the substrate 2 flanked to the MEMSdifferential sensor device 7, and fixed onto the substrate 2, forexample by means of a welding layer 20.

The integrated circuit 19 is electrically coupled to the substrate 2 bymeans of further electric connections 21.

The protective package 14, realized through molding, incorporates theMEMS differential sensor device 7 with the electric connections 13, theintegrated circuit 19 with the further electric connections 21 and thesubstrate 2, leaving the first active surface 11 a of the sensitiveportion 11 of the MEMS differential sensor device 7 exposed through thepassing opening 5 and the second active surface 11 b of the sensitiveportion 11 exposed through the opening 12 of the second surface 10.

Advantageously, the protective package 14 leaves also the lower surface4 of the substrate 2 exposed.

Advantageously, the second surface 10 of the MEMS differential sensordevice 7 is flanked to an upper surface of the protective package 14.

With reference to FIG. 9, the device 1 d of FIG. 6 is shown wherein anintegrated circuit 19 is mounted on the substrate 2 flanked to the MEMSdifferential sensor device 7, and fixed onto the substrate 2, forexample by means of a welding layer 20.

The integrated circuit 19 is electrically coupled to the substrate 2 bymeans of further electric connections 21.

The protective package 14 d, realized through molding, incorporates theMEMS differential sensor device 7, the underfiller 16, the integratedcircuit 19 with the further electric connections 21 and the substrate 2,leaving the first active surface 11 a of the sensitive portion 11 of theMEMS differential sensor device 7 exposed through the passing opening 5and the second active surface 11 b of the sensitive portion 11 exposedthrough the opening 12 of the second surface 10.

Advantageously, the protective package 14 d leaves also the lowersurface 4 of the substrate 2 exposed.

Advantageously, the second surface 10 of the MEMS differential device 7is flanked to the upper surface of the protective package 14 d.

Advantageously, the MEMS differential sensor device 7 used in thedevices according to embodiments of the disclosure is a differentialpressure sensor device shown in FIGS. 10 and 11.

In particular, with reference to these figures, a differential pressuresensor 7 a is shown formed in a semiconductor die 8 a, for example ofsilicon.

In the semiconductor die 8 a a cavity 3 a is realized next to a firstsurface 9 c of the semiconductor die 8 a.

The portion of the semiconductor die 8 a comprised between the cavity 3a and the first surface 9 c forms a membrane 11 c, i.e. the sensitiveelement of the pressure sensor 7 a.

Resistive elements 6 a are formed in the peripheral portion of themembrane 11 c next to the first surface 9 c.

An insulating layer 4 a, for example oxide, coats the first activesurface 9 c of the die 2 a, leaving a first active surface 11 d of themembrane 11 c, comprised between the resistive elements 6 a, exposed.Moreover, openings are provided in the insulating layer 4 a incorrespondence with these resistive elements 6 a for allowing theelectric connection to a conductive layer 2 a which is formed on theinsulating layer 4 a.

Nothing forbids that the insulating layer coats the whole active surface9 c of the die 2 a.

Advantageously, a passivation layer coats the first active surface 9 cof the die 2 a.

In particular, the conductive layer 2 a comprises two portions 2 b and 2c separated from each other and electrically coupled through theresistive elements 6 a.

An opening 12 a, 12 b is provided in a second surface 10 a of the sensor7 a, opposed to the first surface 9 c, which puts the cavity 3 a incommunication with the outside of the sensor 7 a. In this way theopening 12 a, 12 b realizes an access gate for a second pressure whichacts on the second active surface 11 e of the membrane 11 c which isfaced in the cavity 3 a.

As shown in FIG. 10, if the opening 12 a is realized through a dryetching, the walls of the opening 12 a are substantially perpendicularwith respect to the second surface 10 a, i.e. the cross dimensions ofthe opening 12 a are substantially constant.

As shown in FIG. 11 instead, if the opening 12 b is realized through anetching of the wet type the walls of the opening 12 b are tapered, i.e.the cross dimensions of the opening 12 b decrease when departing fromthe second surface 10 a.

In conclusion, with the device according to embodiments of thedisclosure it is possible to realize microphones, pressure, gas,chemical differential sensors, which are encapsulated in a protectivepackage realized through molding.

According to embodiments of the disclosure it is also possible tointegrate more sensors (accelerometers and pressure sensors) in the sameprotective package 14. These packages can be contained in a variety ofdifferent types of electronic systems, such as vehicle safety systems,portable electronic devices like cellular phones and PDAs, video gamecontrollers, computer systems, control systems, and so on.

Advantageously, in a preferred embodiment, the overall electronic device1, 1 a, 1 b, 1 c, 1 d, 1 e, 1 e shows a space comprised between 3×3×1mm^3, while the MEMS differential sensor device 7 shows a width of 1500μm a length of 1500 μm and a thickness 700 μm and shows an opening 12 onthe second surface 10 comprised between 100 and 500 μm.

The sensitive portion 11 of the MEMS differential sensor device 7 is ofcircular or squared shape and has a diameter/side comprised between 100μm and 1000 μm.

The distance between the first surface 9 of the MEMS differential sensordevice 7 and the upper surface 3 of the substrate is comprised between50 and 500 μm, while the thickness of the substrate 2 is comprisedbetween 150 and 300 μm, while the width of the opening 5 is comprisedbetween 100 and 700 um.

If the barrier element 15 is realized by a ring of welding paste it hasa thickness of a cross section comprised between 60 and 300 μm.

If the barrier element 15 a, 15 b is realized by an irregular area, ithas a width of a cross section comprised between 10 and 50 μm and forexample a depth comprised between 20 and 80 μm.

In conclusion, the electronic device according to embodiments of thedisclosure is particularly compact and uses technical solutions which donot provide critical alignments.

Advantageously, the presence of the barrier element 15, 15 a, 15 ballows protection of the sensitive portion 11 of the MEMS differentialsensor device 7 during the manufacturing steps of the protective package14 or during the dispensing step of the underfiller 16 in the electronicdevice 1 according to embodiments of the disclosure.

Advantageously, this barrier element 15, 15 a, 15 b can be of physicalor chemical nature or a combination of the two and can be realized bothon the substrate 2 and on the MEMS differential sensor device 7.

From the foregoing it will be appreciated that, although specificembodiments of the disclosure have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the disclosure.

The invention claimed is:
 1. A method of forming an electronic device,comprising: forming an opening in a substrate having a plurality ofelectrically conductive layers; physically attaching a die to thesubstrate to position a first active surface portion of the die adjacentthe opening of the substrate and, through this physical attachment,electrically connecting the die to at least some of the electricallyconductive layers in the substrate, the die further including a secondactive surface portion exposed through an opening of the die; forming aprotective package to house the substrate and the die, the protectivepackage leaving the opening of the substrate and the opening of the dieexposed; and forming a barrier element surrounding the opening of thesubstrate, the barrier element comprising a ring in contact with thesubstrate and the die, and whose external edge is completely coated bythe protective package; wherein the barrier element is formed fromwelding paste.
 2. The method of claim 1 wherein the operation ofphysically attaching the die to the substrate comprises flip-chipbonding the die to the substrate to thereby provide the physicalattachment and electrical interconnection between the die and theelectrically conductive layers of the substrate.
 3. A method of formingan electronic device, comprising: forming an opening in a substratehaving a plurality of electrically conductive layers; physicallyattaching a die to the substrate to position a first active surfaceportion of the die adjacent the opening of the substrate and, throughthis physical attachment, electrically connecting the die to at leastsome of the electrically conductive layers in the substrate, the diefurther including a second active surface portion exposed through anopening of the die; and forming a protective package to house thesubstrate and the die, the protective package leaving the opening of thesubstrate and the opening of the die exposed; the method furthercomprising forming a barrier element surrounding the opening of thesubstrate, the barrier element comprising an irregular shape in contactwith the substrate and the die, and whose external edge is completelycoated by the protective package.
 4. The method of claim 3 wherein thebarrier element forms an irregular area that extends on an upper surfaceof the substrate to match a sensitive portion of the die.
 5. The methodof claim 4, wherein this irregular area is formed by modifying thechemical properties of the upper surface of the substrate.
 6. The methodof claim 4, wherein this irregular area is formed by non-wettablematerial.
 7. A method of forming an electronic device, comprising:forming an opening in a substrate having a plurality of electricallyconductive layers; physically attaching a die to the substrate toposition a first active surface portion of the die adjacent the openingof the substrate and, through this physical attachment, electricallyconnecting the die to at least some of the electrically conductivelayers in the substrate, the die further including a second activesurface portion exposed through an opening of the die; and forming aprotective package to house the substrate and the die, the protectivepackage leaving the opening of the substrate and the opening of the dieexposed; the method further comprising: coating the die with anon-wettable insulating layer and a protection layer, and forming abarrier element having an irregular area between the substrate and thedie by removing the protection layer from the die and exposing thenon-wettable insulating layer.
 8. The method of claim 7, wherein coatingthe die further comprises coating the die with a polyimide protectionlayer and with an oxide non-wettable material.
 9. A method of forming anelectronic device, comprising: forming an opening in a substrate havinga plurality of electrically conductive layers; physically attaching adie to the substrate to position a first active surface portion of thedie adjacent the opening of the substrate and, through this physicalattachment, electrically connecting the die to at least some of theelectrically conductive layers in the substrate, the die furtherincluding a second active surface portion exposed through an opening ofthe die; and forming a protective package to house the substrate and thedie, the protective package leaving the opening of the substrate and theopening of the die exposed; the method further comprising forming acylindrical projection on the opening of the substrate to facilitate theaccess to the first active surface of the die.
 10. A method of formingan electronic device, comprising: forming an opening in a substratehaving a plurality of electrically conductive layers; physicallyattaching a die to the substrate to position a first active surfaceportion of the die adjacent the opening of the substrate and, throughthis physical attachment, electrically connecting the die to at leastsome of the electrically conductive layers in the substrate, the diefurther including a second active surface portion exposed through anopening of the die: forming a protective package to house the substrateand the die, the protective package leaving the opening of the substrateand the opening of the die exposed; forming a barrier elementsurrounding the opening of the substrate, the barrier element comprisinga ring in contact with the substrate and the die, and whose externaledge is completely coated by the protective package; and formingelectric connections to electrically couple the die to the substrateoutside the barrier element with respect to the first active surface.11. The method of claim 10, further comprising forming an underfillerthat incorporates the electric connections.
 12. The method of claim 11,wherein forming an underfiller that incorporates the electricconnections further comprises forming bumps on the electric connections.